A cleaner is a device that sucks dirt or dust from the floor. As shown in FIGS. 14 and 15, a conventional cleaner includes a suction assembly 20, having a suction nozzle formed therein to suck air, and a main body 10 connected with the suction assembly via a hose that forms a suction passage. The main body 10 is provided with a suction fan that forms negative pressure for sucking air through the suction nozzle, and either the suction assembly 20 or the main body 10 is provided with a dust collector in which the dust sucked through the suction nozzle is collected.
The suction assembly 20 is moved by force that a user applies thereto, and the main body 10 follows the suction assembly 20. When the suction assembly 20 is moved by the user, the main body 10 is dragged by tension exerted on the hose. Recently, a cleaner equipped with a driving motor at a main body has been released. The main body 10 of such a cleaner may be moved by driving force of the driving motor, which is transmitted to wheels and rotates the same.
In this case, traveling wheels 15 are mounted to two opposite side portions of the main body 10, and a pair of driving motors is mounted to the main body 10 to respectively drive the two traveling wheels 15. Rotating force generated by each of the driving motors is transmitted to the corresponding traveling wheel 15 via a plurality of gears G1, G2, G3, G4 and G5. FIG. 14 schematically illustrates spur gears to explain the engagement relationship of the gears G1, G2, G3, G4 and G5. The gears G1, G2, G3, G4 and G5 are tooth-engaged with each other.
Described in detail, the first gear G1 is coupled to a rotating shaft of the driving motor, and the fifth gear G5 is coupled to the traveling wheel 15. When the first gear G1 is rotated by the driving motor, the second to fourth gears G2, G3 and G4 are rotated sequentially, and the fifth gear G5 is finally rotated. The gears constituted in this way enable the traveling wheel 15 to rotate at a reduction gear ratio of n:1 (i.e. while the driving motor rotates n times, the traveling wheel rotates once, where n>1).
The structure in which the rotating force of the driving motor is transmitted to the traveling wheel via the gears is capable of stably increasing a torque and of reducing the transfer of a shock to the rotating shaft of the driving motor because the gears G1, G2, G3, G4 and G5 absorb the shocks applied to the traveling wheel 15 for various reasons, for example, when a user accidentally drops the main body 10 to the floor. However, if the main body 10 is forcibly moved when the driving motor is in an off state (for example, if the main body 10 is manually dragged by tension exerted on the hose when a user moves the suction assembly 20), frictional force between the gears G1, G2, G3, G4 and G5 becomes a cause of inhibiting smooth movement of the main body 10.
For example, as shown in FIG. 15, when the moving direction of the suction assembly 20 is changed while the driving motor is off, a moment is applied to the main body 10 by the tension exerted on the hose. At this time, if the two traveling wheels 15 are smoothly rotated, change of direction of the main body 10 may be easily realized. However, in the process of changing the direction, reaction force acts on the main body 10 in a direction different from the direction in which the main body 10 is pulled by the hose due to frictional force between the traveling wheels 15 and the floor as well as frictional force between the gears G1, G2, G3, G4 and G5, which may occasionally cause a problem in which the main body 10 turns over in the course of changing the direction.
Further, when the main body 10 is forcibly moved at a predetermined speed or more by the tension exerted on the hose, the moving speed of the main body 10 exceeds the rotating speed of the traveling wheels 15, which is determined by the reduction gear ratio, which may cause the main body 10 to slip on the floor and consequently to wobble from side to side.